The present invention relates to a solenoid-controlled valve suitable for use in hydraulic controllers for brakes, for example, an anti-lock brake controller.
One example of conventional solenoid-controlled valves is disclosed in Japanese Patent Application Unexamined Publication (KOKAI) No. 7-144629 (1995). U.S. Pat. Nos. 5,577,815 and 5,609,400 correspond to this Japanese literature. The solenoid-controlled valve has a housing, both ends of which are closed. The housing has a first port and a second port which are provided in a side wall thereof in series from one end toward the other end. A third port is provided at the other end of the housing. A first valve body slides in the housing in a longitudinal direction to bring the first and second ports into and out of communication with each other. A second valve body is placed in the housing so as to be movable in the longitudinal direction to bring the second and third ports into and out of communication with each other. A first spring (first urging member) is interposed between the one end of the housing and the first valve body to urge the first valve body in a valve opening direction. A second spring (second urging member) is interposed between the second valve body and a reduced-diameter portion formed in the housing between the first and second ports to urge the second valve body in a valve closing direction. An electromagnetic force generating device is provided at the one end of the housing. A movable member is engaged with the first and second valve bodies and moved in the housing in the longitudinal direction by an electromagnetic force from the electromagnetic force generating device against urging forces of the first and second springs to cause the first and second valve bodies to move to valve opening or closing positions. The solenoid-controlled valve operates as follows:
{circumflex over (1)} When there is no electromagnetic force from the electromagnetic force generating device, the first valve body is placed in the valve opening position by the urging force of the first spring, and the second valve body is placed in the valve closing position by the urging force of the second spring.
{circumflex over (2)} When the electromagnetic force of the electromagnetic force generating device is set to a first predetermined value, the movable member causes the first valve body to move to the valve closing position against the urging force of the first spring, and the second valve body is placed in the valve closing position by the urging force of the second spring.
{circumflex over (3)} When the electromagnetic force of the electromagnetic force generating device is set to a second predetermined value larger than the first predetermined value, the movable member causes the first valve body to move to the valve closing position against the urging force of the first spring and also causes the second valve body to move to the valve opening position against the urging force of the second spring.
Incidentally, to move the first valve body to the valve closing position in the above-described prior art, it is necessary to generate an electromagnetic force that is sufficiently large to move the first valve body against the urging force of the first spring. To move the second valve body to the valve opening position, it is necessary to generate an electromagnetic force that is large enough to move the second valve body against the urging forces of the first and second springs. Accordingly, the prior art needs to prepare a coil enduring a large electric current or a coil with a large number of turns, resulting in an increase in size of the apparatus. This may make it difficult to ensure a space for installation and also cause an increase in the battery capacity.
With a view to facilitating understanding of the present invention, the known solenoid-controlled valve disclosed in the above-mentioned Japanese Patent Application Unexamined Publication (KOKAI) No. 7-144629 (1995) will be described below with reference to FIGS. 8 and 9 (first prior art) and FIGS. 10 and 11 (second prior art).
As shown in FIG. 8, a solenoid-controlled valve 1 according to the first prior art has a cylinder 4 formed with three ports 3a, 3b and 3c communicating with a cylinder bore 2. Of the three ports 3a, 3b and 3c, two ports are formed in a side wall of the cylinder 4, and the other port is formed in a bottom (right-hand end as viewed in FIG. 8) of the cylinder 4. For the sake of convenience, the ports formed in the side wall of the cylinder 4 are referred to as xe2x80x9ca-port 3a and b-port 3bxe2x80x9d, and the port formed in the bottom as xe2x80x9cc-port 3cxe2x80x9d.
A spool 7 is provided in the cylinder bore 2 so as to be movable with respect to the a-port 3a. The spool 7 has an insertion bore 5 and a passage (spool passage) 6. The spool passage 6 communicates with the insertion bore 5 at one end thereof and opens on the side surface of the spool 7 at the other end thereof. In addition, a poppet valve 8 with an approximately C-shaped sectional configuration is provided in the cylinder bore 2 so as to be movable with respect to the c-port 3c. 
A solenoid 9 is provided at one end of the cylinder 4. A shaft-shaped movable member 10 is provided in such a manner as to be inserted into the solenoid 9. The movable member 10 is driven by the solenoid 9.
The movable member 10 extends through the insertion bore 5 of the spool 7 to reach a hollow portion (no reference numeral) of the poppet valve 8. A projection (referred to as xe2x80x9cfirst projectionxe2x80x9d) 12 is formed at the distal end of the movable member 10. The first projection 12 is engageable with a wall portion 11 of an opening of the poppet valve 8. Another projection (referred to as xe2x80x9csecond projectionxe2x80x9d) 13 is formed on an intermediate portion of the movable member 10. The second projection 13 is engageable with the spool 7.
A spring (first spring) 15 is interposed between the spool 7 and a step portion 14 formed at one end of the cylinder bore 2. The first spring 15 urges the spool 7 toward the other end of the cylinder bore 2. A spring (second spring) 17 is interposed between the poppet valve 8 and a spring retaining portion 16 projecting inward in the cylinder bore 2 between the a-port 3a and the b-port 3b. The second spring 17 presses the poppet valve 8 against the c-port 3c. 
When the solenoid-controlled valve 1 is not energized, the a-port 3a and the passage 6 in the spool 7 are in communication with each other (i.e., the spool 7 is in a valve opening position), and the poppet valve 8 is in a position where it closes the c-port 3c. 
The movable member 10 is displaced according to the value of electric current supplied to the solenoid 9. According to the amount of displacement (stroke) of the movable member 10, valve opening and closing modes of the spool 7 and the poppet valve 8 are changed over as shown in Table 1 below. FIG. 9 shows the relationship between the stroke and the spring force in the operation of the solenoid-controlled valve 1 according to the first prior art.
In FIG. 9 and Table 1: stroke S0 shows an initial position; S1 shows a position where the a-port 3a is closed; S2 shows a position where the first projection 12 is engaged with the poppet valve 8; and shows a predetermined stroke position exceeding S2. The current value increases as the reference range shifts from the first to the second and further to the third.
As shown in FIG. 9, in the stroke range of S0 to S2, the first spring 15 increases in spring force as the stroke becomes longer, whereas the second spring 17 exhibits a constant spring force independently of the displacement of the movable member 10 (solenoid 9). In the stroke range of S2 to S3, both the first and second springs 15 and 17 increase in spring force as the stroke becomes longer. Accordingly, the driving force F to be generated by the solenoid 9 against the first and second springs 15 and 17 increases sharply (this force will hereinafter be referred to as xe2x80x9cdriving forcexe2x80x9d).
The spring force of the second spring 17 acting against the driving force of the solenoid 9 (hereinafter referred to as xe2x80x9canti-solenoid spring forcexe2x80x9d for the sake of convenience) in the stroke range S0 to S3 is as shown by reference symbol T. The anti-solenoid spring force T0 in the stroke range of S2 to S3 (hereinafter referred to as xe2x80x9cfinal stage spring forcexe2x80x9d), which corresponds to the final stage in the stroke range S0 to S3, increases as the magnitude of the spring force of the second spring 17 increases, that is, the stroke increases.
As shown in FIG. 10, the solenoid-controlled valve 1 according to the second prior art has a valve seat (cylinder-side valve seat) 18 for the spool 7. The cylinder-side valve seat 18 projects in the cylinder bore 2 between the a-port 3a and one end of the cylinder bore 2. The first spring 15 is interposed between the movable member 10 and one end (left-hand end as viewed in FIG. 10) of the cylinder 4 to urge the movable member 10 rightward in FIG. 10. The second spring 17 is interposed between the spool 7 and the poppet valve 8 to urge them away from each other.
When the solenoid-controlled valve 1 is not energized, the valve body 19 of the spool 7 is separate from the cylinder-side valve seat 18, and thus the spool 7 is in a valve opening position. In addition, the poppet valve 8 is pressed to close the c-port 3c by the spring force of the second spring 17 and thus placed in a valve closing position. The spool 7 is engaged with a step portion 20 of the movable member 10. Thus, the spool 7 is restrained from moving leftward in FIG. 10.
The movable member 10 is displaced according to the value of electric current supplied to the solenoid 9. According to the amount of displacement (stroke) of the movable member 10, valve opening and closing modes of the spool 7 and the poppet valve 8 are changed over as shown in Table 2 below. FIG. 11 shows the relationship between the stroke and the spring force in the operation of the solenoid-controlled valve 1 according to the second prior art.
In FIG. 11 and Table 2: stroke S0 shows an initial position; S1 shows a position where the valve body 19 of the spool 7 rests on the cylinder-side valve seat 18; S2 shows a position where the first projection 12 is engaged with the poppet valve 8; and shows a predetermined stroke position exceeding S2.
As shown in FIG. 11, in the stroke range of S0 to S1, the first spring 15 increases in spring force as the stroke becomes longer, whereas the second spring 17 expands and thus decreases in spring force as the spool 7 moves leftward in association with the leftward movement of the movable member 10. Accordingly, the driving force F to be generated by the solenoid 9 is expressed by the expression: (spring force of first spring 15)xe2x80x94(spring force of second spring 17).
In the stroke range of S1 to S2, the first spring 15 increases in spring force as the stroke becomes longer, whereas the second spring 17 keeps a predetermined length (i.e., the spring force is constant) because the valve body 19 of the spool 7 rests on the cylinder-side valve seat 18. Accordingly, the driving force F to be generated by the solenoid 9 becomes of magnitude equivalent to the spring force of the first spring 15.
In the stroke range of S2 to S3, the first spring 15 increases in spring force as the stroke becomes longer, and the second spring 17 also increases in spring force because it is pushed by the poppet valve 8. As the result of the increase in spring force of the second spring 17, the driving force F to be generated by the solenoid 9 further increases in comparison to that required in the stroke range of S1 to S2.
In this case, the anti-solenoid spring force T and the final stage spring force T0 of the second spring are as shown by the dashed lines in FIG. 11.
Incidentally, the above-described first prior art suffers from some problems. As shown in FIG. 9, in the stroke range of S2 to S3, both the first and second springs 15 and 17 increase in spring force as the stroke becomes longer (in other words, the final stage spring force T0 assumes a large value). Consequently, the driving force F to be generated by the solenoid 9 becomes extremely large. Therefore, it is necessary to supply a large electric current to the solenoid 9 or to prepare a solenoid 9 with a large number of turns. This causes the apparatus to increase in size and hence makes it difficult to ensure a space for installation. Moreover, the battery capacity may need to be increased. The second prior art also involves problems similar to those of the first prior art. That is, in the stroke range of S2 to S3, the spring force increases (i.e., the final stage spring force T0 assumes a large value) as the stroke becomes longer. Consequently, the driving force F to be generated by the solenoid 9 becomes extremely large. This gives rise to problems as stated above.
In view of the above-described circumstances, an object of the present invention is to provide a compact solenoid-controlled valve requiring a reduced electric current.
The present invention is applied to a solenoid-controlled valve having first and second valve bodies axially movably provided in a bore of a cylinder, a first spring interposed between the cylinder and the first valve body, a second spring interposed between the first and second valve bodies, and an electromagnetic force generating device having a movable member causing the first and second valve bodies to move in association with each other. Valve opening and closing modes of the first and second valve bodies are changed over in a plurality of stages according to the displacement of the movable member.
According to the present invention, the solenoid-controlled valve is provided with a restricting portion for restricting relative displacement of the first and second valve bodies when they are moved away from each other. Therefore, the urging force of the second spring acting against the driving force of the electromagnetic force generating device becomes zero in a valve opening and closing mode in the final stage of the valve opening and closing modes, which modes are changed over in a plurality of stages.
In the present invention, the electromagnetic force generating device may be provided to urge the first and second valve bodies by pushing. Alternatively, the electromagnetic force generating device may be provided to urge the first and second valve bodies by pulling.